The present invention relates to a communication control apparatus between processor systems and, more particularly, to a communication control apparatus suitable for communication through a communication line between a master processor system and a slave processor system which are located at remote positions with respect to each other and having a distance therebetween.
Nowadays, an electronic control is used in controls of various apparatuses and a load of processes to its electronic control is increasing more and more in association with an enlargement in size of the apparatus and complication and advancement of the control. When considering an automobile as an example of such an apparatus, electronic controls are used in the engine control, transmission control, brake control, suspension control, traction control, and the like. To cope with such a large control processing load, one electronic control unit (ECU) is allocated to each of the control processing units or the like.
In case of further advancing the control, it is necessary to transmit and receive information among microcomputers of such a plurality of ECUs. A network system of the vehicle controls is considered. As such a kind of apparatuses, for example, there are examples disclosed in JP-A-1-164203 and JP-A-1-164204. As a communication system between processors existing at remote positions which are used in such a kind of apparatuses, for example, there is a system such that disclosed in JP-A-63-255759 or the like.
As techniques regarding the present invention described later, there are examples as disclosed in U.S. Pat. No. 4,803,613, JP-A-63-101957, and JP-A-1-014605, the contents of which are incorporated herein by reference.
In the above conventional techniques, information that is necessary among a plurality of ECUs connected to a network is communicated on the network in the following manner.
When considering the case where, for example, five ECUs A to E are connected to the network as an example, to impartially generate data from each ECU, it is a general way to generate the data from each ECU to the network in accordance with a predetermined order. Namely, now assuming that the above order is set to, for instance, A, B, C, D, and E, the data is sequentially generated to the network in accordance with the order of the ECUs A, B, C, D, E, A, B, C, D, E, A, B, C, - - - .
In this case, however, while the ECU B is generating the data to the network, even when there occurs a necessity to generate the data which requires an emergency process from the ECU A, the ECU A cannot generate such data to the network until the order of the ECU A comes, namely, until the processes by the ECUs B, C, D, and E are finished, so that there is a problem such that a real-time property (instantaneousness) of the system control is low.
In such a system, as the number of ECUs connected to the network increases, a time interval (waiting time) from a timing when a certain ECU transmitted data to the network to a timing when the ECU can subsequently send data to the network increases, so that the real-time property of the system control further deteriorates.
On the other hand, even when the ECUs do not impartially execute the processes but distributed processes are executed while using the ECU A as a master processor system and using the ECUs B to E as slave processor systems, the ECU A always needs to continuously manage a processing status of each of the ECUs B to E. Therefore, as the number of slave processor systems and the number of tasks which are processed by the slave processor systems increase, the processing capability of the ECU A as a master processor system lacks, so that there occurs a problem such that the real-time manner deteriorates.
The communication control apparatus between processor systems according to the above literature has a problem such that the communication control apparatus doesn't have apparatuses such that when the data from a certain processor system is written as reception data, in a certain memory area in an random access memory (RAM) in the communication control apparatus, the communication control apparatus generates an interruption request, thereby informing such an interruption request to another processor system, so that another processor system cannot promptly respond to the data writing operation.